The present invention relates to heat exchange systems comprising a plurality of internal tubular passageways disposed in a spaced apart relation to each other, which possess utility in heat exchange applications wherein a heat exchange medium is circulated through the passageways. A particular application of such a system resides in devices utilizing solar energy, and specifically, solar energy absorbing devices for elevating fluid temperature.
It is well known that the radiation of the sun can be collected as a source of energy for heating or cooling or for direct conversion to electricity. Heating and cooling depend upon collection of rays of solar energy in a fluid heating transfer system. The heated fluid is pumped or allowed to flow to a place of utilization for the thermal energy it has acquired.
In certain areas of the world, solar energy is the most abundant form of available energy if it could be harnessed economically. Even in more developed areas of the world, the economic harnessing of solar energy would provide an attractive alternative to the use of fossile fuels for energy generation.
One of the problems attending the development of an efficient system for the conversion of solar energy resides with the structure and design of the solar energy absorbing device, or solar collector. This solar collector generally comprises a rectangular plate-like structure possessing channels or passageways for the circulation of the energy absorbing fluid medium. Conventionally, these panels have comprised a pair of opposed expanded passageways, known as headers, which are placed at opposite ends of the panel, and are connected by a plurality of tubular passageways which are often in parallel relation with respect to each other. These passageways, as well as the headers themselves, have generally been disposed at right angles with respect to each other and in parallel relation with respect to the horizontal and vertical dimensions, respectively, of the panel.
Difficulty encountered with known solar collectors relates to the uniformity of distribution of the heat exchange fluid through the several connecting tubular passageways lying between the headers. Though fluid would ideally pass through the individual connector tubes uniformly with respect to velocity, small variations in tube width, tube height and particular travel distance from header to header cause variations in flow rate due to pressure drop through the individual connector tubes. Such variations affect the flow rate and the heat collection rate of the connector tubes and the panel as a whole.
The above problem becomes particularly acute in the instance where collector systems comprising a plurality of panels, which may be placed in either parallel or serial relation to each other are employed. In such systems, the pressure drop experienced within the individual panels is compounded by the pressure drop and unequal flow occurring between the panels as fluid flows from the central manifold or header structure.